Rapid mass ground transportation systems offer many benefits over non-mass transportation means such as the use of automobiles, particularly in metropolitan areas experiencing severe traffic congestion and pollution problems. Mass ground transportation may also be a desirable alternative for short-range as well as long-range air travel. Although there has been a general recognition of the need for a reliable, safe rapid transportation system, utilization of rapid transit systems has been hindered by the high cost of construction and operation as well as technical difficulties in developing an efficient and versatile light rail system.
Conventional approaches have not produced a light rail transportation system that is sufficiently versatile, efficient and cost-effective to be a feasible substitute for non-mass transportation and air travel alternatives. For instance, some so-called light rail systems have rather heavy transportation modules due to the use of heavy undercarriage or a heavy power system, high traction requirements, high on-board fuel requirements, or the like. Systems that rely on traction drives tend to have difficulty with steep grades. Moreover, external elements such as severe weather conditions and contaminations can pose substantial difficulty in the operation and maintenance of light rail systems. Additionally, traction drive mechanisms employing wheels tend to produce a lot of noise as well as wear.
The present inventor's U.S. Pat. No. 6,360,670 B1, which is incorporated herein by reference, overcomes some of these difficulties and disadvantages in an efficient and cost-effective light rail transportation system that uses a guideway system that does not depend on traction for movement. In a specific embodiment disclosed in that patent, the pod assembly is placed inside a guide tube, the exterior of which preferably supports and guides the vehicle as it moves along the tube. Motion is generated by providing a pressure differential inside the tube between the upstream region and the downstream region of the pod assembly. The pressure differential can be generated by a stationary power system that produces a vacuum on the downstream region or pressurizes the upstream region or both. The speed of the pod assembly is controlled by modulating the amount of gas flow through the pod, that is, from the upstream side to the downstream side of the pod. The speed of the pod assembly is increased by reducing the amount of gas flow through the pod assembly to thereby increase the thrust on it, and is decreased by permitting a larger amount of gas to flow past the pod assembly to decrease the thrust.
Because the thrust required to move the pod assembly is generated by stationary power systems, the vehicle does not require heavy on-board engines or drive trains. The pod assembly and guide tube are relatively light in weight and are well-suited for use in a light rail system. The guide tube can be elevated because of the light overall weight of the system, reducing right-of-way costs. When elevated, grading costs and requirements are significantly reduced.
In that earlier patent, a magnetic coupling apparatus is used to couple the pod assembly inside the guide tube with the transportation module outside the guide tube. The use of a magnetic coupling apparatus eliminates the need to mechanically connect the pod assembly and the transportation module with a strut that would otherwise have to extend through a longitudinal opening in the wall of the guide tube. This allows the interior of the guide tube to be a closed system and avoids the need for a seal assembly for maintaining a desired pressure differential in the guide tube as the strut moves through the longitudinal opening of the guide tube, thereby improving mechanical integrity and pressure integrity of the system. Moreover, the use of the magnetic coupling apparatus instead of a mechanical coupling device makes it easier to clean the exterior of the guide tube and coupling apparatus or clear those areas of debris such as the removal of ice and snow. Magnetic coupling also allows disengagement of the pod assembly and transportation module without any mechanical linkage or disengagement. Because the transportation module is supported by the exterior surface of the guide tube, the weight of the transportation module is not carried by the pod assembly.
Although the transportation systems disclosed in U.S. Pat. No. 6,360,670 B1, as well as in related U.S. Pat. No. 6,279,485 and in U.S. Pat. No. 6,267,058, which is also incorporated herein by reference, provide important advances for elevated rail transportation technology, actual tests and theoretical evaluations have shown that some of the components of the system which is the subject of these earlier U.S. patents have certain disadvantages such as, for example, excessive wear or friction, maintenance problems, and the like. The present invention seeks to overcome these disadvantages and provides the improvements discussed below.